ITS-1 ribosomal DNA sequence variants are maintained in different species and strains of Echinococcus

This study investigated sequence heterogeneity in the first internal transc ribed spacer (ITS-1) of ribosomal DNA within and among species and strains of Echinococcus. Different ITS-1 sequence variants exist in Echinococcus gr anulosus and Echinococcus multilocularis, which represent at least four evo lutionary lineages: (1) a sheep strain-lineage of E. granulosus, (2) a sist er lineage of a cervid and camel E, granulosus ITS-1 variants, (3) a lineag e including the ITS-1 variants representing horse, bovine and camel strains of E, granulosus, as well as variants from E. multilocularis, Echinococcus oligarthrus and Echinococcus vogeli and (4) a distinct lineage of ITS-1 va riants including E. granulosus strains from sheep and cervid, and E. multil ocularis. At least two of the species (E. granulosus and E, multilocularis) were paraphyletic for ITS-1. Divergent ITS-1 variants from these two speci es shared distinct evolutionary lineages. The sequence data provided eviden ce that at least two turnover mechanisms. namely slippage and unequal cross ing over/transposition, have led to the divergence and maintenance of seque nce variants in Echinococcus species and strains. (C) 2000 Australian Socie ty for Parasitology Inc. Published by Elsevier Science Ltd. All rights rese rved.